Hi there ... saw a tutorial on this a few weeks ago for making 'leather' luggage tags ! It was actually for air-drying clay, but the principal is the same and looks fantastic ...

Scrunch up a sheet of tin foil, unravel it and flatten it out, then use this as a sort of texture mat for your sugarpaste ... Let it dry out, then it's a case of colouring/tinting and brush work ... Hope that helps - sounds like a fab cake project ! xx